This is a continuation of a multi-faceted project whose overall objective has been to understand the processes involved in gene expression in molecular terms. During its first five years, the project has been concerned with elucidating the structural characteristics of transcriptional and translational control signals and understanding how particular alterations in these signals can affect gene expression. At this time, the project's focus has shifted to an aspect of gene expression that previously has received relatively little attention--namely, the role of mRNA stability in genetic control and the mechanisms by which mRNA turnover occurs. The specific aims for the next period of work are: (1) To identify the structural signals that determine transcript stability or instability, (2) To elucidate the nucleolytic processes involved in mRNA degradation, (3) to understand the mechanisms by which biological processes such as rate of cell growth and translation of mRNA by ribosomes affect mRNA stability, and (4) To elucidate the mechanisms involved in the regulation of gene expression at the level of decay and processing of the rxcA transcript of R. capsulata. Initially, studies will be carried out in the prokaryotic organisms, E. coli and Rhodopseudomonas capsulata; at a later stage in the project, the role of mRNA stability in modulating gene expression within eukaryotic cells will be investigated.